Question:

Published on: 1 October, 2023

**What are flaky and elongated aggregates? How can the shape of aggregate influence strength of concrete? Following is the result of a sieve analysis of 500 gm aggregate:**

IS sieve size |
10 mm |
4.75 mm |
2·36 mm |
1·18 mm |
600 micron |
300 micron |
150 micron |
lower than 150 micron |

Weight retained in gm |
0 |
10 |
50 |
50 |
95 |
175 |
85 |
35 |

**Find out the 'Fineness Modulus' of the sample**

Answer:

**FLAKY AGGREGATES:-** This agg. Are those whose least dimension i.e. thickness is less than 3/5 th of their mean dimension.

**ELONGATED AGGREGATES:-** This agg. are those whose greater dimension i.e. length is greater than 9/5 th of their mean dimension.

** According to shape voids**

Rounded aggregate 32 – 33 %

Irregular aggregate 35 – 38 %

Angular aggregate 38 – 40 %

Rounded aggregate gives better workability and Angular aggregate gives better strength.

total wt. = 500gm.

Sieve | Wt. retained in each sieve(gm) | % wt. retained | cumulative % of wt. retained | % finer |

10 mm | 0 | 0 | 0 | 100 |

4.75 mm | 10 | 2 | 2 | 98 |

2.36 mm | 50 | 10 | 12 | 88 |

1.18 mm | 50 | 10 | 22 | 78 |

600 µ | 95 | 19 | 41 | 59 |

300 µ | 175 | 35 | 76 | 24 |

150 µ | 85 | 17 | 93 | 07 |

<150 µ | 35 | 7 | 100 | 00 |

Ƹ = 346 |

So, F.M. = 346/100 = 3.46

F.M. of coarse aggregate is3.46.

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